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Embryology > Early Embryonic Development > Flashcards

Early Embryonic Development Flashcards

1
Q

_______ increase number of cells in the embryo

A

celavage or mitotic cell divisions

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2
Q

in a blastomere, stage is determined by

A

number of cells

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3
Q

what determines pattern of cleavage

A

yolk volume

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4
Q

what is yolk

A

protein and lipids

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5
Q

isolecithal ova type occurs in

A

most mammals (placenta/marsupials)

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6
Q

isolecithal characteristics

A

small amount of yolk, evenly distributed throughout cytoplasm
holoblastic cleavage

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7
Q

holoblastic cleavage

A

blastomeres divide completely

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8
Q

megalecithal animals include

A

egg laying mammals (platypi, echidna, spiny anteater), birds, reptiles

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9
Q

megalecithal characteristics

A

abundant yolk with embryo forming cytoplasm at the opposite end of zygote

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10
Q

megalecithal animal pole

A

embryo cytoplasm

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11
Q

megalecithal vegetal pole

A

yolk rich cytoplasm

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12
Q

what is meroblastic cleavage

A

cleavage initiated at animal pole, but large yolk mass does not divide (cell division incomplete)

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13
Q

meroblastic cleavage: blastodisc

A

small region of animal pole becomes embryo

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14
Q

meroblastic cleavage: yolk

A

food supply for developing embryo

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15
Q

1st cell division produces

A

2 daughter cells called blastomeres; 2 polar bodies visible

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16
Q

2nd cell division produces

A

4 cell stage (4 blastomeres)

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17
Q

3rd cell division produces

A

8 cell stage (8 blastomeres)

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18
Q

what happens to zona pellucida during these cell divisions?

A

it remains intact and the same size (does not increase in size as the embryo grows)

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19
Q

as long as zona pellucida remains, what happens to cell sizes during each cleavage

A

cell size decreases

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20
Q

what is a morula

A

16-32 cell stage; solid mass of cells

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21
Q

is the zona pellucida intact in a morula?

A

yes

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22
Q

what is the range of the length of time post-ovulation to reach uterus

A

2-8 days

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23
Q

most species time to reach uterus post-ovulation

A

3 days

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24
Q

length of time in dog for post-ovulation to reach uterus

A

8 days

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25
Q

length in time of mare for post-ovulation to reach uterus

A

5-6 days

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26
Q

what are the factors that determine the length of time post-ovulation to uterus

A

amount of smooth muscles in uterine tube
function of fimbrae and cilia
narrowness at ampulla/isthmus junction and uterine tube/uterine horn junction
hormone influence

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27
Q

what does estrogen due to timing post-ovulation to reach uterus

A

slows

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28
Q

what does progesterone due to timing post-ovulation to reach uterus

A

stimulates

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29
Q

the longer it takes to reach uterus,

A

the more number of cleavages are expected and therefore later stage embryo

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30
Q

dog stage when reach uterus

A

blastocyst

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31
Q

feline stage when reach uterus

A

morula

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32
Q

equine stage when reach uterus

A

morula

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33
Q

cattle stage when reach uterus

A

morula

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34
Q

goat stage when reach uterus

A

4-8 cell stage

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35
Q

sheep stage when reach uterus

A

4-8 cell stage

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36
Q

swine stage reach uterus

A

4-8 cell stage

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37
Q

what transforms the morula to a balstocyst

A

a fluid filled space or cavity (blastocoele)

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38
Q

trophoblast

A

outer cell layer, primary source fetal components of placenta

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39
Q

inner cell mass or embryoblast

A

embryo proper

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40
Q

uterine milk or histotroph is

A

secretions of the uterus (enzymes, growth factors, cytokines, hormones, proteins, etc.)

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41
Q

what is the function of uterine milk

A

nourish early embryo until fetal membranes form

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42
Q

zona pellucida prevents _____

A

implantation to protect embryo from female immune system early in development

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43
Q

what is blastocyst hatching

A

rupture/disintegration of zona pellucida

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44
Q

what causes weakening of zona pellucida

A

enzymes by trophoblast and in uterine secretions

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45
Q

rupture of zona pellucida allows _____

A

release of embryo

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46
Q

occurs about day _____

A

4-8

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47
Q

embryo remains ____ until attachment occurs

A

free-floating

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48
Q

transuterine migration

A

movement of early embryo inside lumen of uterus

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49
Q

cow and ewe transuterine migration (with single embryo)

A

minimal

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50
Q

ewe with 2-3 embryos that start in same horn transuterine migration

A

significant

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51
Q

bitch, queen, sow transuterine migration

A

some

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52
Q

mare transuterine migration

A

very extensive, until day 16 or 17

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53
Q

why is transuterine damage so extensive in the horse

A

moves from uterine horn to horn and body several times a day

part of signal to prevent leutolysis and maintain pregnancy

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54
Q

most pregnancies in the hores (66%) eventually implant where?

A

right uterine horn

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55
Q

what is implantation

A

process whereby a fertilized ovum becomes implanted in the lining of the uterus of placental mammals

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56
Q

embryo stages prior to implantation are hardy due to

A

zona pellucida

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57
Q

attachment of trophoblast cells to uterine mucosa can be either _____ or ______

A

nondeciduate or deciduate

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58
Q

nondeciduate is

A

noninvasive

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59
Q

nondeciduate occurs mostly in what species

A

large domestic species

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60
Q

maternal and fetal tissue in nondeciduate

A

loosely apposed (apposed placenta)

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61
Q

separation easily achieved at parturition without _____

A

damage to maternal tissue

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62
Q

deciduate (interstitial) is

A

invasive (destroys uterine mucosa)

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63
Q

what species have deciduate implantation

A

carnivores, rodents, primates

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64
Q

deciduate animals tissue

A

maternal and fetal tissue intimately fused (conjoined placenta)

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65
Q

at birth what happens to maternal tissue

A

maternal tissue is lost

66
Q

bilaminar embryo; trophoblasts move laterally to expose _____

A

inner cell mass

67
Q

inner cell mass flattens to a circular plate consisting of

A

2 layer—>embryonic disc

68
Q

what are the two layers making up the inner cell mass

A

epiblast and hypoblast

69
Q

what is the epiblast

A

outer layer, next to trohpoblast cells

70
Q

what is hypoblast

A

inner layer, lines inside of epiblast and trophoblast cells

71
Q

what is gastrulation

A

process by which bilaminar embryo is converted into a trilaminar embryonic disc, creating 3 primary (primitive) germ layers

72
Q

what are the 3 layers

A

ectoderm, mesoderm, endoderm

73
Q

ectoderm

A

exterior most

74
Q

mesoderm

A

middle

75
Q

endoderm

A

internal most

76
Q

primitive streak

A

caudal marginal zone of epiblast induces fomration; extends caudal —–> cranial

77
Q

ectoderm color coding

A

blue

78
Q

mesoderm color coding

A

red

79
Q

endoderm color coding

A

yellow (us) green (europe)

80
Q

primitive node

A

increased concentration of cells found at the cranial end

81
Q

primitive streak establishes

A

craniocaudal axis of developing embryo, median plane, and right-left patterns

82
Q

initiation site for gastrulation

A

migration of epiblast cells toward primitive streak
cell ingress to end up between epiblast and hypoblast
epiblasts give rise to all 3 primative germ layers for the embryo

83
Q

ectoderm

A

nervous tissue, epidermis

84
Q

mesoderm

A

skeleton, muscle, connective tissue, circulatory system, urinary and much of reproductive system

85
Q

intraembryonic mesoderm

A

body of embryo (from epiblast)

86
Q

splanchnic

A

viscera

87
Q

somatic

A

body wall

88
Q

extraembryonic

A

outside embryo, embryonic membranes (from hypoblasts)

89
Q

endoderm

A

digestive glands, GI epithelium, respiratory epithelium

90
Q

intraembryonic

A

body of embryo

91
Q

extraembryonic

A

outside embryo, embryonic membranes

92
Q

what is a notochord

A

dense column of mesodermal cells on midline, formation initiated at primitive node

93
Q

notochord becomes a reference axis for

A

developing embryo

94
Q

what is the driving force for growth and development

A

cell signaling

95
Q

cell growth

A

increase in cell size

96
Q

cell proliferation

A

mitosis to increase cell numbers

97
Q

induction

A

one group of cells stimulates (induces) differentiation of an adjacent group of cells

98
Q

differentiation

A

a cell or group of cells progressively develop specific structural and functional roles based on their physiological and biochemical attributes

99
Q

what is patterning

A

establishment of programmed subsets of cells in proper relationship to each other and surrounding cells and tissues. Necessary for normal tissue and organ formation

100
Q

what is migration

A

cells move from one area of the embryonic (or fetal body) to a different area

101
Q

cell death (programmed cell death)

A

cells removed in a precisely regulated manner; genetically controlled

102
Q

what are twins

A

two individuals which develop in the same pregnancy in animals that are normal monotocous (bear a single offspring)

103
Q

polytocous

A

bear many offspring in a single pregnancy

104
Q

twins in sheep and goats

A

is the goal!

105
Q

twins in cattle ranges from _____ to ____ of births

A

3 to 9%

106
Q

cattle twins increases with what

A

assisted reproduction technologies (hormone treatments, embryo transfer)

107
Q

when twins naturally occur in cattle, it si typically _____

A

dizygotic

108
Q

horse twins is most common cause of

A

non-infectious abortion

109
Q

twin blastocysts during transuterine migration

A

typically one is lost

110
Q

horse twins when both implant….

A

typically both abort, live birth extremely rare

111
Q

horse twins when born

A

high neonatal mortality due to immature development

112
Q

dizygotic twins result from

A

two different ova (usually developed from separate follicles) and each is fertilized independently and each embryo develops independently

113
Q

dizygotic twins has _____ zygotes and ____ genotypes

A

different; different

114
Q

in dizygotic each has what

A

own set of fetal membranes, but membranes and fetal vessels can fuse allowing exchange of blood between fetuses

115
Q

are dizygotic twins hereditary

A

yes

116
Q

monozygotic twins results from

A

a single zygote that separates into 2 zygotes in early cell division

117
Q

monozygotic twins are ______ zygotes and ______ genotype

A

2 different zygotes; 1 genotype (first zygote splits early on when cells could become anything)

118
Q

monozygotic embryos each have

A

own set of fetal membranes

119
Q

duplication of inner cell mass (bilaminar embryo)

A
  1. short fetal membranes separate (aminon) others shared (yolk sac and chorion (chorioallantois)
120
Q

bilaminar embryo documented in

A

sheep and pig, but not cattle, and 70% of human monozygotic twins

121
Q

duplication of primitive streak in monozygotic twins

A
  1. shared fetal membranes

2. documented in mouse and chicken (1% of human monozygotic twins)

122
Q

what are the rules for classification of twins

A

genetic identity
degree of separation
symmetry of separation

123
Q

genetic identity

A

dizygotic (2 genotypes) vs. monozygotic (identical genotypes)

124
Q

degree of separation can be

A

free or conjoined

125
Q

free

A

embryo/fetuses completely separated from each other

126
Q

conjoined

A

embryo/fetuses attached to one another

127
Q

conjoined twins are ____ in origin

A

monozygotic in origin and represent an incomplete separation between the 2

128
Q

symmetry of separation can be classified as

A

symmetrical or asymmetrical

129
Q

symmetrical

A

equal size/body parts, duplication of body axis

130
Q

asymmetrical

A

unequal size, extra body parts without duplication of body axis

131
Q

freemartins

A

extraembryonic vessels of twins anastomose allowing exchange of fluid between fetuses before sexual differentiation;
one twin is XX (female) and other is XY (male)
female fetus affected by hormones (antimullerian duct hormone and testosterone) of male twin fetuses

132
Q

most common intersex condition is a

A

pseudohermaphodite (sterile)

133
Q

masculinization of female tract in pseudohermaphodite)

A

external genitalia, female but reduced in size except for enlarged clitoris (small vulva, enlarged clitoris, encreased anogenital distance)
gonads look like testes and form seminiferous tubules, produce no sperm, cell are genetically X
short, blind-ended vagina (1-4 week old calves; normal 13-15 cm; freemartin 5-6 cm)
cervix absent

134
Q

what are free symmetrical monozygotic twins

A

genetically identical twins (derived from single zygote)

not attached to each other in any way

135
Q

separation typically between,

A

2 cell blastomere and blastocyst stage, generally 2 separate sets of fetal membranes form

136
Q

free assymetrical twins may be

A

monozygotic or dizygotic

137
Q

free asymmetrical twins are not _____

A

physically connected by body parts, but vascular systems interconnected

138
Q

in free asymmetrical twins, what are the twins like

A

one twin is normal, other is underdeveloped

139
Q

terms to describe undeveloped twin

A

amorphout globusus
anidian fetus
acaardiac fetus
holocardius

140
Q

why does the undeveloped twin survive

A

because of connection to blood supply

141
Q

characteristics of undeveloped twin

A

non-distinct body form, disorganized collection of tissues (skin, muscle, teeth, rudimentary GI organs)

142
Q

human

A

twin reveresed arterial perfusion or TRAP sequence

143
Q

twin to twin transfusion

A

exchange of blood between free twins

144
Q

undeveloped twin heart

A

underdeveloped and not fully

145
Q

circulation od undeveloped twin is driven by

A

normal twin

146
Q

in free asymmetrical twins, the normal twin is

A

pumping blood for 2fetuses

147
Q

this can lead to

A

heart failure in fetal life and intrauterine death (human mortality rat is 50%)

148
Q

conjoined symmetrical twins

A

incomplete separation of monozygotic twins, typically in primitive streak stage, duplication of body axis

149
Q

where is primitive streak duplicated?

A

at cranial or caudal end, but fails to divde completely

150
Q

diplopagus

A

nearly complete, connected by a small amount of tissue

151
Q

dicephalus

A

2 heads

152
Q

diprosopus

A

2 tails

153
Q

tetrabrachius

A

2 pair of thoracic limbs

154
Q

tetrasccelus

A

2 pair pelvic limbs

155
Q

conjoined assymetrical twins

A

incomplete separation of monozygotic twins, marked unequal size or without duplication of body axis

156
Q

extra body parts are of the conjoined fetus are typically

A

smaller and misshapen

157
Q

mummified fetus is not necessarily a

A

twin fetus phenomenon

158
Q

mummified fetus occurs when

A

a normal fetus arrests in fetal development and dies

159
Q

the mummified fetus becomes ____ in uterus

A

dehydrated and shrunken

160
Q

a mummified species should not be mistaken for ______ in twin pregnancies

A

an underdeveloped, free symmetrical twin

Embryology (18 decks)

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